Continuous process for the manufacture of lead-sodium alloys



Nov. 15, 1955 H. H. WALL, JR 2,723,913

CONTINUOUS PROCESS FOR THE MANUFACTORY OF LEAD-SODIUM ALLOYS Filed Dec. 6, 1951 2 Sheets-Sheet l FIGURE Nov. 15, 1955 H. H. WALL, JR

CONTINUOUS PROCESS FOR THE MANUFACTORY OF LEAD-SODIUM ALLOYS 2 Sheets-Sheet 2 Filed Dec. 6, 1951 R Md 3 T L a mu W 1H 2 M 6 N M F Y n B .m 6 3 A w 9 F 5.0 Y 3m 5 6 8 7 6 5 4 3 0 a 7 6 5 88888M88N777M Q 1m 8. C has: Mk Kb Q Hui J r United States-Patent C) CONTINUOUS PROCESS FOR THE MANUFACTURE OF LEAD-SODIUM ALLOYS Application December 6, 1951, Serial No. 260,121

7 Claims. (Cl. 75-167) This invention relates to the maufacture of chemically active alloys of lead. In particular, the invention relates to the preparation of lead-sodium metal alloys such as are used in the manufacture of organo-metallic compounds, e. g., tetraethyllead and the other alkyl compounds of lead.

Heretofore, various means have been used for the preparation of the alkali-metal-alloys, all of these methods involving the preparation of large batches of the alloy in a large so-called manufacturing pot. It has been thought necessary to carry out the manufacture in this manner, because of several reasons. The sodium component of such alloys is very reactive and even though it is protected from the atmosphere by an inert gas, still some degradation of the alkali metal frequently occurs.

tions of alkali metals, it has been necessary to follow a batch procedure. It was thus necessary to blend a large batch of alloy in approximately correct proportions, then to analyze a sample of the batch, and then to make ap-- 'propriate adjustments as necessary. This has been .particularly true in producing monosodium-lead alloy, NaPb, this alloy having 10 Weight percent sodium at its stoichiometric composition. As an example of the prior techniques found necessary in manufacturing batches of such alloy, Fisher et al. Patent 2,276,031, discloses a procedure for mixing these two components, wherein a ffportion of the lead is charged to the manufacturing pot first, and. following that addition the remaining amount of lead and all of the sodium are charged prior to the mixing analysis and adjustment of sodium content. Precautions in making the alloy by this technique were considered essential, because the alloy, NaPb, is, in fact, a chemical compound, and it was thought essential for subsequentvusage that it correspond almost identically to that composition. The method of making this alloy jhe retofore used has frequently been a limiting step in 'the manufacture of'organo-metallics derived from such alloys, and very cumbersome and complicated equipment and much operating labor has been essential. As an example of the equipment required for such installations, Amick, U. S. Patent 2,043,224, describes typical apparatus. Additional factors hitherto complicating the preparation of sodium-lead alloys are the large ditferences in the densities of the two components, sodium having a density of about unity, and lead having a density of 'l1.3 grains per milliliter. Another factor significant in these binary systems is the heat of reaction or heat of 'mixingincurred in their preparation. Thus, the heat of mixing of sodium and lead to produce one pound mole of the monosodium-lead alloy is approximately 16,000 B. t. u.s, which will raise the temperature of the alloy approximately 800 F;

An object of the invention is to provide a continuous process for the manufacture of sodium-lead alloys of .uniform and precise-composition. A'more specific object is to provide a process whereby alloys are produced hav- Hence, and especially since the alloys desired. normally contain only realtively small weight concentraing predetermined performance characteristics, in particular assuring high yields of alkyllead compounds in subsequent processing, Without the necessity of analysis and adjustment of the composition of large batches of alloy. Another object is to provide a process whereby the components of alloy are continuously mixed and apportioned in response to a physical factor correlative with the desired performanceattributes. An additional object is to provide-integrated apparatus for carrying out the process. A still further object is to provide apparatus whereby the process is performed automatically when desired.

In its broadest form, the process comprises the continuous feeding together of molten lead and molten sodium, the flows thereof being apportioned to provide a uniform density at a constant temperature of the .concurrently, then the so-formed alloy is passed through a constant volume zone and concurrently weighed therein, the initial feeds of sodium and lead being apportioned responsive to variations in weight of the alloy in the constant volume zone to provide a substantially constant weight.

The general method of the process as well as the preferred embodiments are more fully explained in detailed description hereafter given and with reference to the figures. Figure 1 is a schematic flow diagram also showing the relative disposition of the apparatus for a preferred automatic embodiment of the process. Figure 2 illustrates the effectiveness with which the performance of a'sodium-lead alloy, as a feed material for ethylation processes, is ascertainable from the reciprocal of the specific volume, being a plot of the yield obtained in the ethylation of alloys of varying density. Figure 3. is a sectional elevation of preferred apparatus for jointly feeding the sodiumand lead to the process. I

The benefits of the process are made possible by the findings that the yield ofan alkyllead product is related to the density of the molten alloy at a given temperature. Further, in the'region of maximum yield, the density is within a range sufiiciently great that it provides a particularly elfective property for assuring a high and uniform yield. Referring to Figure 2, .a plot is given of the yield of tetraethyllead obtainable in the ethylation of alloys of varying density. The yield represents the eificiency of sodium utilization by the equation:

4NaPb 4C2H Ol PbCCzlEkh. 3Pb -l- 4Na01 Alloy Ethyl Chloride Tetraethyllead Lead SodiumChlorlde The plot of this figure is based upon the results of a series 'of ethylations of comminuted solid sodium-lead '5.87 or above about 6.0. It is thus seen that a high and satisfactory yield of tetraethyllead, varying only about one-half of one percent, is obtained when alloys having a density of 5.87 to 6.0 are employed. This range amounts to a variation of about two percent of the through line 26 to alloy manufacture.

j surrounded by insulation therein.

and its housing or mounting is supported by a scale 15.

n cal -1transmitting a controlling energy impulse, either electrilevel by a predetermined degree. are limit switches in effect.

mean density of the alloy, which is easily attained by the present process.

A preferred embodiment of the process is describedv hereafter with reference to Figure 1. Referring to the figure, the main units of apparatus include a sodium supply tank 10, a lead supply tank 11, a heat exchanger 13, and a weighing coil 33, supported upon a scale 15. Sodium is fed to the supply tank through line 16 from a manufacturing source. A centrifugal pump 17 of the submerged or acid type discharges sodium through line 18 to a small head tank 19, at which point the sodium flow is split to a portion recycled to the supply tank 10 through line 20, the main portion being fed through line 21 to the alloy formation steps.

Lead is intermittently charged through line 49 as desired to the lead supply tank 11. The lead in pot or tank 11 is pumped out by centrifugal pump 22 through line 23 to head tank 24, splitting from this point to a recycle portion in line 25, and a portion being fed In operation, the flow of lead is set at a constant value by valve 27.

e The sodium and lead are fed together at connection 28 and pass into heat exchanger 13, where a coolant is supplied through line 29 from coolant tank 9. The

coolant, preferably a eutectic mixture of diphenyldiphenyl oxide is circulated at a rate suificient to maintain the discharge temperature of the alloy at a constant level. The discharge temperature is ascertained by a thermocouple 30 in discharge line 31 and functions as the control variable for control of the coolant flow by valve 32. Upon discharge of the mixed metals from the heat exchanger 13, the alloy passes to the weighing coil 33, which is contained in a housing 14, and is preferably The weighing coil Any minute variations in the overall weight of this as- 's'ernbly, including the alloy passing through the weighing coil 33 is thus reflected by deflection of the scale 15.

In operation the scale indication or indicating device actuates an instrument or controller 34 of'conventional type.

This instrument, which may be combined with a recorder, may be a pneumatic transmitter, or an electriimpulse transmitter. Such devices provide for the alloy within the coil 33 so that the proportion of sodium metal should be increased. Accordingly, the -transmitter 34 would then transmit electrical or pneumatic force by line or wire 36 to the motor actuated 'valve 12 to increase the rate of sodium flow. Trans- .mission lines or wires 35 and 37 lead from the transmitter 34 to a control or cut-out switches on the drives for the feed pumps 17 and 22. These pressure transmitters are safeguards, in that they, would provide for "shutoff of the pump drives if the weight of the coil 33 and contents either exceeded or was below a standard In other words, these Thus, if the drive for. pump 22 had failed so that only pure sodium was flowing to .ithe-coil 33 and hence it would fall far below the desired weight, it would be impossible to adjust the process and obtain correct composition by adjustment of the valve in the normal manner. Hence, a shutoff of the sodium feed pump 17 is provided. Alternatively, if the sodium drive pump fails, the controller and transmitting line 37 will be arranged to shut off completely the flow of lead by pump 22. During a steady state operation only the adjustment of control valve 12 is varied, so that the total weight of the alloy in weighing coil 33 is maintained constant within fairly narrow limits. The alloy which is continuously discharged from the weighing coil 33 passes through line 38 to storage tank '39 wherein it is continuously agitated by agitator 40. A delivery pump 41 transmits finished alloy as needed through line 42 to subsequent ethylation operations.

As a further feature of the apparatus, provision is of course made for preventing freezing of either the feed metals or the product alloy at any point in the apparatus. Various appropriate means are conventional for this purpose. Thus, the lead and alloy conduits are suitably fitted with induction type electrical heaters, and the sodium supply line or conduit is fitted with electrical resistance heaters. It is also essential that constant volume coil 33 should be completely filled with the metal in process. This is assured by appropriate elevation of the discharge conduit 38 from the weighing coil 33. In order to prevent freezing of the alloy in the weighing coil 33, insulation is provided, as heretofore mentioned, so that the temperature of the alloy does not appreciably drop in this equipment. One or more drain valves are customarily provided at the lowermost points in the system. This assures that the apparatus can be completely drained of alloy or supply metal during shutdowns.

As previously mentioned, the alloy mixture discharged from heat exchanger 13 is maintained at a uniform tem perature. Control of the inlet temperature to the weighing coil 33 assures that the weight measurement therein need not be corrected for temperature variation which affects the density of the alloy itself. The coolant for the alloy in preparation is preferably a few degrees above the freezing temperature of the alloy, thereby assuring that there will be no pluggage in the heat exchanger 13. Coolant is discharged from heat exchanger through line 43 and is itself cooled in .coil 44 by water distributed by line 45 and a spray head 46. The flow of water for this purpose is adjusted by automatic valve 47, maintaining the temperature of the coolant liquid constant as determined by thermocouple 48.

As an example of operation of a preferred embodiment such as described above, lead is fed through line 26 at a rate of about 8100 pounds per hour and at a temperature of 750 F. The sodium is fed through line 21 at a rate, controlled by a valve 12, of about 900 pounds per hour. The two metal streams are fed together at the inlet to heat exchanger 13 and in passing therethrough the temperature first rises, owing to the heat of mixing, but is then reduced by coolant flow to about 750 F. The stream then passes through weighing coil 33, which is an elongated pipe holding about 1000 pounds of alloy, or about seven minutes production. The product hold up vessel normally contains about 40,000 pounds of alloy, but capacity is provided for approximately twice this quantity. The controller 34 is adjusted to provide adjustment of the sodium flow, by valve 12, in response to variations of the weight of the coil 33 and housing 14 above or below the weight corresponding to an average density therein of 5.95 at 750 F. The alloy delivered through line 38 is easily thus maintained in the density range 5.87 to 6.0, and the normal hold up in the product receiver 39 further smooths out the density of the product delivered to succeeding operations through line 42.

7 Although the process is of greatest benefit in the preparation of sodium-lead alloys of composition approximating the monosodium alloy NaPb, the principles are fully applicable to preparation of the other alloys, containing, for example 15 or 20 percent sodium.

It, willbe understood that numerous alternatives in the process are possible in addition to the above described alent results are obtained in this manner, but normally it is preferred to control the sodium flow as necessary.

do, ia

Inasmuch as the, sodium has a density of about l, its

flow inthe liquid phase is somewhat more susceptible to precise control by conventional valves.

Although it is preferred to carry out the mixing and cooling operations concurrently, as described with reference to Figure 1, such concurrence is not absolutely essential to the process. If desired, these steps may be carried out discretely. As an example of such a procedure, the sodiumv and lead streams are fed to a small mixing pot fitted with a propeller type or an anchor type motor driven agitator. Sufiicient agitation is provided so that the two components are thoroughly mechanically mixed at discharge, the discharge line preferably being at a point relatively remote from the feed points. Thus, when the sodium and lead are introduced at the top of such a mixing pot, the discharge point is desirably located at the bottom. As no provision is made for removing the heat of mixing in such an embodiment, a subse quent heat exchanger receives the overflow from the mixing pot and cools it to the desired temperature prior to transfer to the constant volume coil or chamber used in continuously following the'density of the, alloy product. As the heat exchanger in such an embodiment does not necessarily perform a mixing function, its design is somewhat simplified in that the only criterion of operability is the removal of the necessary heat at design conditions. i

In the preferred embodiments wherein the mixing and cooling are carried out concurrently, it is desirable to introduce or feed together the lead and the sodium in a nozzle or feed assembly providing a central stream'of sodium and a surrounding annular stream of lead. Apparatus particularly suitable in this-regard is illustrated in Figure 3. Referring to Figure 3, a tube 50 in the heat exchanger-mixer has a feed assembly mounted in its inlet comprising an annular shell 53 and a central tube 51. Sodium is supplied through the central tube 51 and lead is supplied through the feed line 52 to the shell 53. The discharge opening 54 for the lead supply is formed by the shell 53 and the central or sodium supply tube 51. In practice, the relative areas of these openings are such that the linear velocities of the sodium and lead are approximately equal. In passing through the heat exchange tube 50, formation of a uniformly mixed liquid alloy is facilitated in that only transverse dispersion of the two components is required. This is readily achieved through the turbulence created by the thermal forces resultant from the heat of mixing and the turbulence accompanying flow through the heat exchange conduit 50 It is obviously advantageous to achieve automatic operation of the process, as exemplified by the embodiment of Figure 1, heretofore described. The principal objects of the process are, however, fully attainable by manual control of the feed components. Thus, for

example, in the embodiment illustrated by Figure 1, if manual control is desired, valve 12 in the sodium feed line is manually adjusted in response to variations in the weight of alloy in the coil 33 as indicated by the scale 15.

It is practical when necessary to discharge the completed alloy directly from the continuous weighing operation to subsequent operations utilizing the alloy. Thus, in the embodiment illustrated by Figure 1, it is entirely feasible to pass the alloy discharged from coil 33 through line 38 to a consuming process, e. g., the manufacture of tetraethyllead. It is, however, customary and preferred to provide a product accumulator or hold up tank 39. By providing vigorous agitation and suflicient volume of product in such a vessel, several desirable results are achieved. Firstly, even the small variations in product density which can occur are further minimized by the bulk dilution effect of the alloy in the hold up tank 39. In addition, such a reservoir provides a dual assurance to continuity of operations. Thus, if the consuming process is shut down, capacity is provided for hold if the alloy producing operation is interrupted, this reservoir provides a continuing supply of feed alloy to the following consuming process.

Having described in full the process and the preferred embodiments thereof, what I wish to claim by Letters Patent is:

1. A continuous process for the manufacture of a molten alloy of sodium and lead comprising feeding together a stream of molten sodium and a stream of molten lead at relative rates controlled as hereafter defined, passing the so-formed stream of sodium and lead through an elongated mixing zone, mixing therein without externally supplied agitation and concurrently cooling the so-formed alloy to a constant temperature above the melting point of the alloy, then passing the'alloy through a constant volume zone and continuously weighing thealloy in said zone and altering the relative rates of the sodium and lead in response to the weight of the alloy within said constant volume zone, the relative rate of sodium feed being increased when the weight of the alloy in the constant volume zone rises above a predetermined value and being decreased when the weight of the alloy falls below a predetermined value. I

2. A continuous process for the -manufacture of a molten alloy of sodium and lead comprisingfeeding together a stream of molten sodium and a stream of molten lead at relative rates controlled as hereafter defined, passing the combined streams through an elongated mixing zone, mixing therein without externally supplied agitation and concurrently cooling the so-formed alloy to a constant temperature above the melting point of the alloy, then passing the alloy through a constant volume zone and continuously weighing the alloy in said zone and altering the relative rates of the. sodium and lead in response to the Weight of the alloy in said constant volume zone, the relative rate of feed of sodium to lead being increased when the weight of the alloy in said zone increases above a predetermined value and being decreased when the said weight decreases below a predetermined value, then collecting the alloy in a pool of previously formed alloy having a volume appreciably greater than the volume of the alloy within the constant volume zone, and vigorously mixing therein, concurrently Withdrawing alloy from said pool at a rate approximately equivalent to the feed rate thereto.

3. A continuous process for the manufacture of a molten alloy of sodium and lead comprising feeding together a stream of molten sodium metal and a stream of molten lead metal at approximately equal lineal rates, the relative rates being controlled as hereafter defined, passing said combined streams through an elongated mixing and cooling zone, mixing the sodium and lead therein without externally supplied agitation and concurrently removing the heat of mixing and cooling to a predetermined temperature above the freezing point of the alloy, then passing the so-formed alloy through a constant volume zone and continuously weighing the alloy within said constant volume zone and altering the relative rates of the sodium and lead in response to the weight of the alloy within said constant volume zone, the relative rate of sodium feed being increased when the weight of the alloy in the constant volume zone rises above a predetermined value and being decreased when the weight of the alloy falls below a predetermined value.

4. A continuous process for the manufacture of a molten alloy of sodium and lead comprising providing a stream of molten lead at a constant rate, feeding a stream of molten sodium into the molten lead stream at approximately the same lineal rate, passing said combined streams through an elongated mixing and cooling zone, mixing the sodium and lead therein without externally supplied agitation and concurrently removing the heat of mixing and cooling to a predetermined temperature above the freezing point of the alloy, then passing the so-formed alloy through a constant volume zone and concurrently weighing the alloy within said constant volume zone "and increasing the rate of sodium feed when the weight of the alloy rises above a predetermined value and destream of molten lead at a constant rate, feeding concentrically thereto a stream of molten sodium at approxi- -mately the same lineal rate, passing said combined streams through an elongated mixing and cooling zone, mixing the sodium and lead therein without externally supplied agitation and concurrently removing the heat of mixing and cooling the so-formed alloy to a predetermined temperature above the freezing point of the alloy,-then passing the alloy through a constant volume l zone and concurrently weighing the alloy within said constant'volume zone and adjusting the rate of the sodium Efed to the lead in response to the weight of the alloy in the constant volume zone, increasing the rate of sodium ted when the weight increases above a predetermined va'lue, and decreasing when the weight decreases below '-'a predetermined value.

6. A continuous process for preparing a liquid monosodium lead alloy suitable for preparation of tetraethyllead or the like comprising feeding together a stream of molten sodium'and a stream of molten lead at relative rates adjusted as hereafter defined, passing the so-formed :stream through an elongated mixing zone, mixing therein without externally supplied agitation and concurrent- -ly cooling the so-formed alloy to a temperature of about 750 F., then passing the alloy through a constant volume zone and continuously weighing the alloy in said zone and decreasing the relative rate of sodium when the said alloy 3 weight decreases below the weight corresponding to a density of 5.87 grams per milliliter, and increasing the relative rate of sodium when the said alloy weight increases above 6.0 grams per milliliter.

7. An'apparatus for the production of a molten alloy of sodium and lead having a lead supply conduit and valve and a sodium supply conduit and valve, a feed nozzle connected to said supply conduits, the feed nozzle having chambers for feeding together the sodium and lead in the same direction and at approximately equal lineal velocities, an elongated mixing and cooling conduit connected to said nozzle and receiving the sodium and lead delivered by the nozzle, cooling means associated with the elongated conduit for cooling the sodium and lead while mixing therein the so-formed alloy to a predetermined temperature above the melting point of the so-formed alloy, and upwardly directed elongated constant volume chamber connected to the cooling and mixing conduit for receiving the alloy therefrom, weighing means and means operatively connected to the constant volume chamber and to one of the valves for regulation of flow responsive to changes in weight of the contents of the elongated chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,815,347 Cowles et al. July 21, 1931 2,036,950 Meyer Apr. 7, 1936 2,083,391 Murray June 8, 1937 2,091,801 Amick et al Aug. 31, 1937 7 2,100,315 Harper Nov. 30, 1937 2,366,075 Weyandt Dec. 26, 1944 2,459,618 Cartier Jan. 18, 1949 OTHER REFERENCES Instruments for Measuring and Controlling Process Variables, Chem. and Met. Engineering, May 1943, pages 108-124. 

1. A CONTINUOUS PROCESS FOR THE MANUFACTURE OF A MOLTEN ALLOY OF SODIUM AND LEAD COMPRISING FEEDING TOGETHER A STREAM OF MOLTEN SODIUM AND A STREAM OF MOLTEN LEAD AT RELATIVE RATES CONTROLLED AS HEREAFTER DEFINED, PASSING THE SO-FORMED STREAM OF SODIUM AND LEAD THROUGH AN ELONGATED MIXING ZONE, MIXING THEREIN WITHOUT EXTERNALLY SUPPLIED AGITATION AND CONCURRENTLY COOLING THE SO-FORMED ALLOY TO A CONSTANT TEMPERATURE ABOVE THE MELTING POINT OF THE ALLOY, THEN PASSING THE ALLOY THROUGH A CONSTANT VOLUME ZONE AND CONTINUOUSLY WEIGHING THE ALLOY IN SAID ZONE AND ALTERING THE RELATIVE RATES OF THE SODIUM AND LEAD IN RESPONSE TO THE WEIGHT OF THE ALLOY WITHIN SAID CONSTANT VOLUME ZONE, THE RELATIVE RATE OF SODIUM FEED BEING INCREASED WHEN THE WEIGHT OF THE ALLOY IN THE CONSTANT VOLUME ZONE RISES ABOVE A PREDETERMINED VALUE AND BEING DECREASED WHEN THE WEIGHT OF THE ALLOY FALLS BELOW A PREDETERMINED VALUE. 